Method of flameproofing cellulosic wallboard and article produced thereby



Patented Aug. 11, 1953 METHOD OF FLAMEPROOFING CELLULOSIC WALLBOARD ANDARTICLE PRODUCED THEREBY Harold C. OBrien, Jr., Beaver, Pa.

No Drawing. Application May 24, 1949, Serial No. 95,159

14 Claims.

This invention relates to a method of treating cellulosic materials andmore particularly to a method of flameproofing cellulosic wallboard. Bythe term fiameproofing is meant the treating of the material so that itwill not readily ignite and will not propagate flame under ordinaryconditions.

Cellulosic wallboard has attained considerable commercial importance inthe building and other industries where its structural and insulatingqualities can be used to good advantage. However, wallboard, like allcellulosic materials is subject to destruction by fire and willpropagate flame under ordinary conditions. In modern fireproof buildingconstruction, it is essential that the combustible character of suchcellulosic wallboards be altered so that propagation of flame isdifiicult if not impossible.

Cellulosic materials have in the past been treated to fiameproof them byimpregnating them with materials such as chlorinated paraffin,chlorinated rubber or other chlorinated hydrocarbons, borates andcertain other salts which decompose when heated. I have found howeverthat these procedures do not constitute a satisfactory solution of theproblem, and, moreover, that their use as heretofore proposed may bepositively dangerous in that they give a false sense of security. Animpregnating treatment ought to result in a permanent fiameproofing ofthe material, and users will generally assume that it does so. Myobservations, however, show that the treatment may be relativelyshort-lived, in terms of the normal life of the impregnated material. Myobservations also show that many of the materials which have beenproposed may have a destructive action on the cellulosic materialitself.

My invention provides a flameproofing treatment which under all expectedconditions of use will persist throughout the expected life of theimpregnated material and hence will not become a deceptive fire trap,and which does not undesirably impair the structural strength and otherphysical properties of the impregnated material.

My treatment comprises two steps; first, impregnating the board with amixture of substantially neutral fiameproofing substances and thencoating or covering the surface of the board with a vapor impervious andflame-resisting sealing preparation. It is feasible to treat wallboardby my method so that the impregnating salts will not leach out over anextended period of time, even in a relatively moist location, thusmaking wallboard available for use in locations where it was previouslybelieved to be unsuitable.

The primary impregnation solution which I have used is a substantiallyneutral aqueous solution of water soluble fire retarding agents. It isessential that this material have a high degree of penetration. Thishigh degree of penetration may be brought about by the addition of awetting agent.

As an example of a satisfactory impregnant, I have used an aqueoussolution of ammonium sulfamate and sodium tetraborate and a wettingagent and treated the wallboard so as to incorporate about one-eighthpound of each of these substances per square foot of one-half inchcellulosic wallboard. Impregnation was effected by soaking the board ina hot aqueous solution F. to F.) containing approximately 7;; parts ofwater and 1.175 parts each of-ammoni-umsulfamate and sodium tetraborateand a suitable. wetting agent which reduced the soaking time forcomplete impregnation. The board was allowed to remain in the solutionuntil saturated. It was then heated to evaporate the water. The totalweight of the resulting dried board was increased about 25% of drysolids.

After the impregnated board was dried the surface was painted with acoating preparation having fiameproofing properties as well as providinga vapor seal. The material which was used for-v the coating was anorganic sol of pyrobitumen. This material is resistant to flame and mayhave incorporated within it a pigment, such as finely divided metallicaluminum, to produce a more attractive surface as well as to increasethe resistance of the coating to flame.

I have found that the wetting agents manufactured and sold by Carbideand Carbon Company under the names Tergitol F G, which is a 25% aqueoussolution of the sodium salt of 2- ethyl hexene l-sulfonic acid, andTergitol #7, which is a 25% solution of the sodium salt of 3-9 diethyldi-decanol 6 sulfate, are most satisfactory for my process although tothe best of my knowledge any wetting agent would be satisfactory.

The effectiveness of my fiameproofing process appears to depend for itsefiiciency upon several difierent principles, all closely related to thephysical and chemical properties of the flameproofing substances. In theimpregnating mixture, the ammonium sulfamate, an organic preparation,liberates ammonia gas when heated apparently choking the flame by asmothering blanket of ammonia gas. Sodium tetraborate, on the otherhand, fuses when heated and appears to form a protective incombustiblemolten flux coatingthe fibers of the board, thereby repelling the flamesfrom the surface of the cellulosic fibers. The two materials ammoniumsulfamate and sodium tetraborate also act to neutralize each other uponhydrolysis thus preventing injury to the wallboard by chemical action ofthe impregnating material when the wallboard becomes clamp. The coatingmaterial, an organic sol of pyrobitumen, sold under the trade-name ofRoskote Resins, by Royston Laboratories, Inc., contains a majorproportion of ultra divided solid highly polymerized and non-ereactive:aspha-ltene particles which are fairly saturated hydrocarbon materialsprimarily napthanic in nature. The major portion of these colloidalparticles are under .01 micron in diameter. This material is relativelyfree from inorganic contamination and from reactive organic constituentssuch as oil and low molecular weight fractions. Freedom from inorganiccontaminants is especially important for the presence of such materialscauses the coating film to be subject to attack by acids or alkalies.Such inorganic materials are also readily leached out of the coating bymoisture causing permeation and reduction of the vaporsealing and insu-'lating qualities of the film. Air dried films of ""Roskote Resin areresistant to strong inorganic acids such as sulphuric andhydrochloricpthey are non-saponifiable by strong alkalies such as sodiumhydroxide; and they resist Weathering and oxidation and maintain theirphysical properties from sub-zero temperatures to above 500 degreesFahrenheit. These coatings may be pigmented with metallic or metallicoxide pigments such as titanium dioxide, zinc oxide, cobalt oxide andoxides of iron to modify the physical properties. For example, aluminumpigmentation results :in a film resistant to a temperature of 800degrees Fahrenheit.

Insulating board or wallboardwhen treated according to the process of myinvention will char but will not burn with a flame when subjected tointense heat such as the fiame of a blowtorch. It is not affectedby thepresenceof moisture. There is no deterioration of the fiameproofingproperties of the impregnating materials or the coating material overlong periods of time. The wallboard, when treated according to myinvention, retains its basic desirable physical properties plus theadditional properties of flame and moisture resistance.

While I have described a present preferred application of my invention,it may be otherwise embodied or practiced within the scope of thefollowing claims.

I claim:

1. A method of treating cellulosic materials comprising the steps ofimpregnating the cellulosic material with ammonium sulfamate and sodiumtetraborate by immersing the wallboard until saturated in a hot aqueoussolution of about '7 partswater and about 1.75 parts each of sodiumtetraborate and ammonium sulfamate, substantially removing the wateradded by the impregnating solution and-coating the surface of the driedmaterial with an organic sol of pyrobitumen, the major portion of whichhas a particle size-less than 0.01 micron indiameter.

2. A method of treating cellulosic materials comprising the steps ofimpregnating the cellulosic material with ammonium .sulfamate and sodiumtetraborate by immersing the wallboard tially removing :the water .added:by the :impreglulosic material with ammonium sulfamate and sodiumtetraborate by immersing the wallboard until saturated in a hot aqueoussolution of about '7 parts Water and about 1.75 parts each of sodiumtetraborate and ammonium sulfamate, substantially removing the wateradded by the impregnating solution and coating the surface of the driedmaterial with a suspension of finely divided 'metallic aluminum in anorganic sol of pyrobitumen, the major portion of which has a particle.size less than 0.01 micron in diameter.

4. A method of treating cellulosic materials comprising the steps ofimpregnating the cellulosic material With a substantially neutralsolution of ammonium sulfamate and sodium tetraborate, heating theimpregnated material to;substantially remove the diluent added by theimpregnating solution, and coating the surface :of the dried materialwith an organic sol of pyrobitumen lsubstantially free of water-solubleinorganic contaminants.

5. A method of treating cellulosic wallboard comprising the steps ofimpregnating the cellulosic material with a substantially neutralsolution of ammonium sulfamate and sodium tetraborate, heating theimpregnated material to substantiall remove the moisture added by theimpregnating solution, and coating the surface of the dried materialwith a suspension of a finely divided metallic pigment in an organic solof pyrobitumen substantially free of water-soluble inorganiccontaminants.

6. A method of treating cellulosic wallboard comprising the steps ofimpregnating the cellulosic material with a substantially neutralsolution of ammonium sulfamate and sodium tetraborate, heating theimpregnated material to substantially remove the moisture added by theimpregnating solution, and coating the surface of the dried materialwith a suspension of a finely divided metal in an organic sol ofpyrobitumen substantially free ef water-soluble inorganic contaniinants.

7. A method of treating cellulosic materials comprising the steps ofimpregnating the cellulosic material with a substantially neutralaqueous solution of an ammonium compound which is solid at roomtemperatures but which liberates ammonia .gas when heated to thecombustion temperature of the cellulosic material and alsorate which isfusible at the combustion temperature of the cellulosic material,substantially removing the moisture added. by the aqueous ,impregnatingsolution and coating the surface of the dried material with an organicsol of pyrobitumen substantially free of water-soluble inorganiccontaminants.

8. A flame-resistant wallboard comprising a sheet of cellulosic materialimpregnated with substantially equal parts of ammonium sulfamate andsodium tetraborate and coated with a .vapor impervious andflame-resistant coating .of .pyrobitumen having an average particle sizeless than 0.01 micron in diameter.

9. A flame-resistant wallboard comprising a sheet of cellulosic materialimpregnated with ammonium sulfamate and sodium tetraborate and coatedw-ith a vapor impervious and flame-resistant coating of pyrobitumensubstantially free of water-soluble inorganic contaminants.

10. A method of treating cellulosic wallboard comprising the steps ofimpregnating the wallboard with an aqueous solution of an ammoniumcompound which is solid at room temperature but which liberates ammoniagas when heated to the combustion temperature of the cellulosic materialand a borate which is fusible at the combustion temperature of thatmaterial, the ammonium compound and the borate being in such proportionsas to form a substantially neutral solution, substantially removing thewater added with the impregnating solution and coating the surface ofthe dried material with an organic sol of pyrobitumen substantially freeof water-soluble inorganic contaminants and having a major portion ofits particles less than 0.01 micron in diameter.

11. A method of treating cellulosic wallboard as claimed in claim 5wherein the metallic pigment is a metal oxide.

12. A method of treating cellulosic materials comprising the steps ofimpregnating the cellulosic material with a substantially neutralaqueous solution of an ammonium compound which is solid at roomtemperatures but which liberates ammonia gas when heated to thecombustion temperature of the cellulosic material and a borate which isfusible at the combustion temperature of the cellulosic material,substantially removing the moisture added by the aqueous im- HAROLD C.OBRIEN, JR.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,418,730 Ottman June 6, 1922 1,926,253 Allen Sept. 12, 19332,097,509 Boller Nov. 2, 1937 2,142,115 Cupery Jan. 3, 1939 2,568,849Fasold et al Sept. 25, 1951 FOREIGN PATENTS Number Country Date 563,996Great Britain Sept. 8, 1944 OTHER REFERENCES Abraham-Asphalts and AlliedSubstances, vol. 1, pp. 57, 724, I31, 740, and 741, 5th Ed., 1945-D. VanNostrand Co., Inc., New York city, N. Y.

7. A METHOD OF TREATING CELLULOSIC MATERIALS COMPRISING THE STEPS OFIMPREGNATING THE CELLULOSIC MATERIAL WITH A SUBSTANTIALLY NEUTRALAQUEOUS SOLUTION OF AN AMMONIUM COMPOUND WHICH IS SOLID AT ROOMTEMPERATURES BUT WHICH LIBERATES AMMONIA GAS WHEN HEATED TO THECOMBUSTION TEMPERATURE OF THE CELLULOSIC MATERIAL AND A BORATE WHICH ISFUSIBLE AT THE COMBUSTION TEMPERATURE OF THE CELLULOSIC MATERIAL,SUBSTANTIALLY REMOVING THE MOISTURE ADDED BY THE AQUEOUS IMPREGNATINGSOLUTION AND COATING THE SURFACE OF THE DRIED MATERIAL WITH AN ORGANICSOLE OF PYROBITUMEN SUBSTANTIAL FREE OF WATER-SOLUBLE INORGANICCONTAMINANTS.